Drilling rod and drilling method

ABSTRACT

A drill rod for reverse circulation drilling, the drill rod including a first outer tube having an first end adapted to receive a rotational force to transfer the rotational force to the first drill bit and a second end adapted to receive a first drill bit, and a first inner tube adapted to be inserted in the outer tube to define an annulus to allow fluid flow from the first end of the outer tube to the second end of the outer tube, the inner tube having a first end and a second end, the second end being adapted to receive a second drill bit, wherein the inner tube is releasably inserted within the outer tube. An inner string for a drill rod, and method for casing a borehole also are disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Australian Patent Application No. 2012905255, filed on Dec. 3, 2012, the disclosure of which is incorporated herein in its entirety by reference.

TECHNICAL FIELD

The present invention relates to methods and apparatus for drilling boreholes.

The invention has been devised particularly, although not necessarily solely, in relation to methods and apparatus for conducting reverse circulation drilling.

BACKGROUND ART

The following discussion of the background art is intended to facilitate an understanding of the present invention only. The discussion is not an acknowledgement or admission that any of the material referred to is or was part of the common general knowledge as at the priority date of the application.

Air rotary drilling methods are used to create in relative short periods of times boreholes in the ground. Reverse drilling is an example of an air drilling method.

Reverse drilling (RC drilling) is typically used for recovering samples from the ground into which the borehole is drilled. This method uses a hollow rod that has an inner tube fitted inside it. The air is delivered to a bit through a side entry swivel and through a gap between the drill rod and inner tube (also called annulus). The samples of the soil that is being drilled are delivered via the air to the surface. The samples pass through the centre of the bit into the inner tube for delivery to the surface. At the surface the samples are passed through a top swivel and into a cyclone where the samples are separated from the air. The advantages of RC drilling is that it is possible to obtain accurate samples from the bottom of the borehole that are not contaminated by the side walls of the hole which have been drilled. This is because the sample is delivered to the surface via the inner tube.

Typically, after having drilled the hole it desirable to obtain a representation of the stratigraphic formation of the ground into which the hole has been drilled. The stratigraphic formation of the ground is conducted by lowering into the hole a probe to analyse the composition of the soil of the side walls of the hole.

Prospecting of the side walls of the borehole to obtain a representation of the stratigraphic formation of the ground is typically conducted by extracting the outer rod and the inner tube from the borehole after the borehole has been drilled. After the extraction of the outer rod and the inner rod the borehole needs to be cased. This can be done via a casing such as a tube which is lowered into the hole after removal of the drill rod (the inner tube and the outer tube).

Typically, casing a borehole is a cumbersome process. This is particularly true in view that to design a appropriate casing it is necessary to take into account, for example, the subsurface data such as formation pressures, strengths and makeup of the subsurface.

It is against this background that the present invention has been developed.

SUMMARY OF INVENTION

According to a first aspect of the invention there is provided a drill rod for reverse circulation drilling, the drilling rod comprising an outer tube having an upper end adapted to receive a rotational force to rotate the outer tube and a lower end adapted to receive the drill bit to transfer the rotational force to the drill bit and in fluid communication with the drill bit, and an inner tube adapted to be inserted in the outer tube, wherein the inner tube is releasably attached within the outer tube.

Preferably, the inner tube being in fluid communication with the drill bit,

Preferably, the inner tube comprises first and second end portions, the first and second end portions comprising means to centre the inner tube within the outer tube. This allows to locate the inner tube coaxially with respect to the outer tube.

Preferably, the means to centre the inner tube within the outer comprises a plurality of protrusions extending radially outward from the circumference of the first and second end portions. In this manner, the arrangement of protrusions defines a spacer which allows defining an annulus between the inner tube and the outer tube. The annulus being in fluid communication with the drill bit to provide fluid such as air to the bottom of the borehole that is being drilled.

Preferably, the protrusions are arranged in a spaced apart arrangement around the circumference of first end second end portions such as to define a plurality of clearances, each of the clearances being located between neighbouring protrusions. The clearances allow fluid flow longitudinally within the annulus defined between the outer tube and the inner tube.

In one arrangement there are two clearances located opposite to each other and two vertical flat surfaces located opposite to each other, the two clearances being located between neighbouring protrusions and the two flat surfaces located between neighbouring protrusions.

Preferably, the flat surfaces are adapted to be gripped by jaws of a gripping tools such as a spanner tool. This allows applying a rotational force to the inner tube as well as holding and moving the inner tube.

Preferably, each protrusion protrudes substantially perpendicularly from the circumference of the end portions defining first and second surfaces which extend radially outward from the circumference of the end portions.

Preferably, the first surface comprises a horizontal surface and the second surface comprises an inclined surface.

Preferably, the horizontal surface comprises a flat surface, adapted to support the jaws of the gripping tool. This allows holding and moving longitudinally the inner tube within the outer tube.

In a particular arrangement there are a plurality of inner tubes adapted to be attached together to define an extended inner tube adapted to be received by an extended outer tube comprising a plurality of outer tubes adapted to be attached together to define the extended outer tube.

Preferably, each of the first end portions of each inner tube comprises means for attaching the second end portions of an inner tube adjacent to the each inner tube.

Preferably, the first end portion comprises a female junction and the second end portion comprises a male junction adapted to be received by the female junction.

Preferably, the female junction comprises an inner thread and the male junction comprises an outer thread for screwing the female and male junction together after insertion of a portion of the male junction into a portion of the female junction.

In a particular arrangement, the drill rod comprises a first inner tube adapted to be attached within the outer tube at the bottom of the borehole.

Preferably, the first inner tube is adapted to receive the extended inner tube which is releasably attached within the outer tube.

Preferably, the drill rod further comprises first and second end portions adapted to be attached to each other, the second end portion being adapted to be attached to the first inner tube and the first end portion being adapted to be attached to the extended inner tube which is releasably attached within the outer tube.

Preferably, the first and second end portions are adapted to be releasably attached to each other.

Preferably, the first and second end portions are adapted such that a relative large force needs to be applied in order to attach (or unattach) the first and second end portions together.

Preferably, the first and second end portions comprise means to impede rotational movement between the second end portion and the first end portion.

Preferably, the means to impede rotational movement comprise at least one leg extending from the first end portion and a plurality of lugs located in a spaced apart relationship around the second end portion defining a lug arrangement, the lug arrangement being adapted to receive the at least one leg.

According to a second aspect of the invention there is provided an inner tube of a drill rod for reverse circulation drilling, the inner tube being adapted to be releasably inserted in an outer tube, wherein the inner tube comprises first and second end portions, the first and second end portions comprising means to centre the inner tube within the outer tube.

Preferably, the means to centre the inner tube within the outer tube comprises a plurality of protrusions extending radially outward from the circumference of the first and second end portions of the inner tube.

Preferably, the protrusions are arranged in a spaced apart arrangement around the circumference of first end second end portions such as to define a plurality of clearances, each of the clearances being located between neighbouring protrusions.

In one arrangement there are there are two clearances located opposite to each other and two vertical flat surfaces located opposite to each other, the two clearances being located between neighbouring protrusions and the two flat surfaces located between neighbouring protrusions.

Preferably, the flat surfaces are adapted to be gripped by jaws of a gripping tool such as a spanner tool.

Preferably, each protrusion protrudes substantially perpendicularly from the circumference of the end portions defining first and second surfaces which extend radially outward from the circumference of the end portions.

Preferably, the first surface comprises a horizontal surface and the second surface comprises an inclined surface.

Preferably, the horizontal surface comprises a flat surface, adapted to support the jaws of the gripping tool.

According to a third aspect of the invention there is provided an end portion for an inner tube for a drill rod for reverse circulation drilling, the inner tube being adapted to be releasably inserted in an outer tube, wherein the end portion comprises means to centre the inner tube within the outer tube.

Preferably, the means to centre the inner tube within the outer tube comprises a plurality of protrusions extending radially outward from the circumference of the end portion.

Preferably, each protrusion protrudes substantially perpendicular from the circumference of the end portion defining first and second surfaces which extend radially outward from the circumference of the end portion.

Preferably, the first surface comprises a horizontal surface and the second surface comprises an inclined surface.

In an arrangement, the end portion comprises a female junction comprising an open end having an inner thread.

In an alternative arrangement, the end portion comprises a male junction having an open end comprising an outer thread adapted to screw onto the thread of the inner thread of the female junction.

Preferably, in the arrangement of the female junction the horizontal surface defined by the protrusions faces towards the open end having the inner thread.

Preferably, in the arrangement of the male junction the inclined surface defined by the protrusions faces towards the open end having the outer thread.

Preferably, the male junction comprises an extended portion adapted to be received by the open end of the female junction. The extended portion facilitates alignment of the female and male junction prior screwing of the male and female junction.

According to a fourth aspect of the invention there is provided a junction for joining first and second tubes, the junction comprising first and second end portions adapted to be attached to each other, the second end portions being adapted to be attached to the first tube and the first end portion being adapted to be attached to the second tube which is releasably attached within the outer tube.

Preferably, the second tube comprises the inner tubes in accordance with the second aspect of the invention.

Preferably, the first and second end portions are adapted to be releasably attached together.

Preferably, the first and second end portions are adapted such that a relative large force needs to be applied in order to attach (or unattach) the first and second end portions to each other.

Preferably, the first and second end portions comprise means to impede rotational movement between the second end portion and the first end portion.

Preferably, the means to impede rotational movement comprise at least one leg extending from the second end portion and a plurality of lugs located in a spaced apart relationship around the first end portion, the lugs defining a lug arrangement being adapted to receive the at least one leg.

According to a fifth aspect of the invention there is provided a tool comprising a handle and a head attached to the handle, the head comprising an indentation adapted to receive a tube, the indentation having an inner edge comprising a flange which at least partially surrounds the inner edge, wherein the flange is adapted to receive a first surface of at least one protrusion protruding from the circumference of a tube to secure the tube to the tool.

Preferably, the tube comprises the inner tube in accordance with the second aspect of the invention.

Preferably, the indentation is adapted to receive the at least one protrusion of the tube to allow application of a rotational force to the tube

According to a sixth aspect of the invention there is provided a drill rod for reverse circulation drilling, the drilling rod comprising a first outer tube having an first end adapted to receive a rotational force to transfer the rotational force to the first drill bit and a second end adapted to receive a first drill bit, and a first inner tube adapted to be inserted in the outer tube to define an annulus to allow fluid flow from the first end of the outer tube to the second end of the outer tube, the inner tube having a first end and a second end, the second end being adapted to receive a second drill bit, wherein the inner tube is releasably inserted within the outer tube.

Preferably, the drill rod further comprises a coupling for transferring the rotational force to the second drill bit, the coupling adapted to releasably couple the first inner tube to the first outer tube.

Preferably, the coupling comprises a drive sub and a driven gear, the drive sub being releasably attached to the first outer tube and the driven gear being releasably attached to the first inner tube, the drive sub being adapted to releasably couple the inner tube to the outer tube

Preferably, the drive sub is releasably attached to the first end of the first outer tube and the driven gear being releasably attached to the first end of the first inner tube.

Preferably, the drill rod further comprising a seal between the second end of outer tube and the second end of the inner tube to impede fluid from exiting the annulus and the second end of the inner tube comprising at least one port to allow fluid to flow from the annulus into the inner tube to form a vacuum so as to transport soil samples into the inner tube to a location distal from the first and second drill bits.

Preferably, the at least one port comprises an angled port to direct the fluid in a direction opposite to the first and second drill bits.

Preferably, the first inner tube comprises a protruding structure to centre the inner tube within the outer tube.

Preferably, the centring structure comprises a plurality of protrusions extending radially outward from the circumference of the first and second ends, the protrusions being arranged in a spaced apart arrangement around the circumference of the first end second ends.

Preferably, the drill rod further comprises a plurality of clearances between neighbouring protrusions and a plurality of surfaces between neighbouring protrusions, the clearances being located opposite to each other and the surfaces being located opposite to each other.

Preferably, the drill rod further comprises further comprising a plurality of second inner tubes adapted to be sequentially attached to each other and to the driven gears, and a plurality of second outer tubes adapted to be sequentially attached to each other and to the drive sub.

Preferably, each of the second inner tubes comprises the centring structure for centring the inner tube within the outer tube.

According to a seventh aspect of the invention there is provided an inner string of a drill rod for reverse circulation drilling, the inner string comprising an inner tube, the inner tube being adapted to be releasably inserted in an outer tube, the inner tube and the outer tube defining an annulus between the inner and outer tube.

Preferably, the inner tube comprises first and second ends, the first and second ends comprising centring structure for centring the inner tube within the outer tube,

Preferably, the drill string further comprises driven gear having an end attached to the first end of the inner tube, the driven gear being adapted to receive a rotational force from the outer tube for rotation of a drill bit attached to the second end of the drill bit.

Preferably, the driven gear is adapted to releasably couple the inner tube to the outer tube.

Preferably, the drill string further comprises at least one additional inner tube comprising a centring structure for centring the inner tube within an outer tube, the driven gear having an opposite end attached to the additional inner tube.

Preferably, the second end of the inner tube comprises at least one port to allow fluid to flow from the annulus into the inner tube to define a vacuum at a location adjacent the second end of the inner tube.

Preferably, the at least one port comprises an angled port.

According to an eight aspect of the invention there is provided a drill rod for reverse circulation drilling, the drill rod comprising a first outer tube having an first end adapted to receive a rotational force to transfer the rotational force to the first drill bit and a second end adapted to receive a first drill bit; a first inner tube adapted to be inserted in the outer tube to define an annulus to allow fluid flow from the first end of the outer tube to the second end of the outer tube, the inner tube having a first end and a second end, the second end being adapted to receive a second drill bit; and a seal means between the second end of outer tube and the second end of the inner tube to impede fluid from exiting the annulus and the second end of the inner tube comprising at least one port to allow fluid to flow from the annulus into the inner tube to form a vacuum so as to transport soil samples into the inner tube to a location distal from the first and second drill bits.

Preferably, the at least one port comprises an angled port to direct the fluid in a direction opposite to the first and second drill bits.

According to a ninth aspect of the invention there is provided a drill rod for reverse circulation drilling, the drill rod comprising a first outer tube having an first end adapted to receive a rotational force to transfer the rotational force to the first drill bit and a second end adapted to receive a first drill bit; a first inner tube adapted to be inserted in the outer tube to define an annulus to allow fluid flow from the first end of the outer tube to the second end of the outer tube, the inner tube having a first end and a second end, the second end being adapted to receive a second drill bit; and a coupling for transferring the rotational force to the second drill bit, the coupling adapted to releasably couple the first inner tube to the first outer tube, wherein the coupling is releasably attached to the inner and outer tubes.

Preferably, the coupling comprises a drive sub and a driven gear, the drive sub being releasably attached to the first outer tube and the driven gear being releasably attached to the first inner tube, the drive sub being adapted to releasably couple the inner tube to the outer tube

Preferably, the drive sub is releasably attached to the first end of the first outer tube and the driven gear being releasably attached to the first end of the first inner tube.

According to an tenth aspect of the invention there is provided a drill rod, the drill rod comprising a first outer tube having an first end adapted to receive a rotational force to transfer the rotational force to the first drill bit and a second end adapted to receive a first drill bit, and a first inner tube adapted to be releasably inserted within the outer tube.

According to an eleventh aspect of the invention there is provided a drill rod for reverse circulation drilling, the drilling rod comprising a first outer tube having an first end adapted to receive a rotational force to transfer the rotational force to the first drill bit and a second end adapted to receive a first drill bit; a first inner tube adapted to be inserted in the outer tube to define an annulus to allow fluid flow from the first end of the outer tube to the second end of the outer tube, the inner tube having a first end and a second end, the second end being adapted to receive a second drill bit; and a seal means between the second end of outer tube and the second end of the inner tube to impede fluid from exiting the annulus and the second end of the inner tube comprising at least one port to allow fluid to flow from the annulus into the inner tube to form a vacuum so as to transport soil samples into the inner tube to a location distal from the first and second drill bits.

Preferably, the at least one port comprises an angled port to direct the fluid in a direction opposite to the first and second drill bits.

According to an twelfth aspect of the invention there is provided a method for casing a borehole after drilling thereof, the method comprising the steps of:

-   -   inserting at least one first inner tube in an outer tube having         a lower end adapted to receive a first drill bit, the inner tube         having a lower end adapted to receive a second drill bit;     -   releasably coupling the inner tube to the outer tube to transfer         rotational force from the outer tube to the second drill bit;     -   drilling the borehole using the outer tube incorporating the         inner tube; and     -   extracting the inner tube from the outer tube.

Preferably, the method further comprises the steps of inserting a pipe within the outer tube and extracting the outer tube.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features of the present invention are more fully described in the following description of several non-limiting embodiments thereof. This description is included solely for the purposes of exemplifying the present invention. It should not be understood as a restriction on the broad summary, disclosure or description of the invention as set out above. The description will be made with reference to the accompanying drawings in which:

FIG. 1 is a perspective view of a section of the drill rod in accordance with an embodiment of the invention;

FIG. 2 is a top perspective view of an inner tube of the drill rod shown in FIG. 1;

FIGS. 3 and 4 are front perspective views of first and second end portions of the inner tube show in FIG. 2;

FIGS. 5 and 6 shows the process for joining together a plurality of inner tubes show in FIG. 2;

FIG. 7 is a perspective view of the outer tube of the drill rod shown in FIG. 1 including the inner tube shown in FIG. 2;

FIG. 8 is a top view of a spanner tool in accordance with an embodiment of the invention;

FIGS. 9 to 11 show the process of engagement of one of the end portions shown in FIGS. 3 and 4 to the tool shown in FIG. 8;

FIG. 12 a is a schematic side view of a cross section of a drill rod in accordance with a first arrangement of an embodiment of the invention showing a plurality of inner tubes joined together via end portions;

FIG. 12 b is a schematic side view of a cross section of a drill rod in accordance with a second arrangement of an embodiment of the invention showing a plurality of inner tubes joined together to a first inner tube via an alternatives arrangement of end portions;

FIG. 13 are front perspective views of first and second end portions of the inner tube in accordance with an embodiment of the invention;

FIG. 14 is a front perspective view of the end portions shown in FIG. 13 in assembled condition;

FIGS. 15 a, 15 b and 15 c are perspective views showing the process for securing an additional inner tube to an inner tube located in a borehole;

FIG. 16 is a perspective view of a spanner in extended condition for securing an outer tube to a rotary table of a drill rig;

FIG. 17 is a perspective view of the spanner shown in FIG. 16 in retracted condition;

FIG. 18 is a perspective view of a spanner engaged with a rod;

FIG. 19 is a perspective view of a spanner disengaged from a rod;

FIG. 20 is a perspective view of a rotary table and rod arrangement;

FIG. 21 is a perspective view of a spanner, accessory spanner and table arrangement;

FIGS. 22 to 24 are perspective views showing the process for separating an inner tube from an inner string incorporated within an outer string;

FIG. 25 is a perspective view of a drive sub from the box thread end;

FIG. 26 is a side perspective view of drive means of the inner tube;

FIG. 27 is a perspective view of the drill bit of the outer tube; and

FIG. 28 is a perspective view of a drill bit showing ports.

DESCRIPTION OF EMBODIMENTS

In accordance with the present embodiment of the invention, there is provided a drill rod 10 to conduct, for example, RC drilling. The drill rod 10 comprises an inner tube 12 and an outer tube 14. The inner tube 12 is adapted to be inserted in the outer tube 14 to define an annulus 16 (see FIG. 7). The annulus 16 allows for air to be delivered from the upper surface of the ground to the drill bit. The air and samples of the bottom of the borehole produced during drilling of the borehole are delivered to the surface through the inner tube 12.

Referring to FIGS. 27 and 28, in accordance to a particular arrangement of the present embodiment of the invention, the air is delivered from the annulus 16 to the inner tube 12 through a plurality of ports 120. In the arrangement shown in the figures the ports 120 are located on the drill bit 92 of the inner tube 12. In alternative arrangements the ports 120 may be located on locations adjacent to the drill bit 92.

The ports 120 traverse the wall 122 of the inner tube 12 in such a manner that the air flow forms a vacuum at the bit face. This vacuum allows lifting of the soil samples. In the arrangement shown in FIG. 28 the ports 120 are angled to direct the air flow into the inner tube and upwards to the upper surface.

Furthermore, there is provided seal means for impeding the air from flowing through the gap defined between the drill bit of the outer tube 14 and the inner tube 12. The seal means close the gap between the drill bits 92 and 94 so as to direct the air through the ports 122 and into the inner tube 12. FIG. 27 shows a close up of the dill bit 94 incorporating the seal means. In the particular arrangement shown in FIG. 27, the seal means comprises a annular seal 124 supported in an annular recess 126. The annular seal 124 extends around the inner periphery of the outer tube 14 a and adjacent to the drill bit 94. In this manner, when the inner tube 12 a is inserted in the outer tube 14 a the lower portion of the inner tube 12 a abuts the annular seal 124. This seals the gap defined between the lower end of the outer tube 14 and lower end of the inner tube 12. Thus, the air flowing through the annulus is directed into the angled ports and into the inner tube to form the vacuum for lifting of the soil samples.

We refer now to FIGS. 12 a and 12 b, in the arrangement in accordance the present embodiment of the invention there is provided an inner string 11 and an outer string 13, wherein the inner string rod 11 is releasably located within the outer string rod (see FIGS. 12 a and 12 b). It is particularly advantageous that the inner string rod 11 is releasably located within the outer string rod 13 because it allows extraction of the inner string rod 11 after completion of drilling of the borehole leaving the outer string rod 13 within the borehole. The fact that the outer string rod 13 is left within the borehole after extraction of the inner string rod 11 allows, for example, the outer string rod 13 to functions a the casing of the borehole. Thus, there is no need for the drilled borehole to be cased in view that the outer string rod 13 has been left within the borehole to act as a casing. The passage defined by the outer string rod 13 allows a prospecting probe to be lowered into the borehole to establish the composition of the formation in which the borehole has been drilled or for further drilling operation to extract, for example, core samples from the earth formation by lowering a core drill through the outer string 13 for generating a core sample. This is particular useful during diamond drilling.

In an alternative arrangement, instead of maintaining the outer string rod 13 within the borehole to maintain the integrity of the borehole it is possible to insert a pipe 90 (see FIG. 24) into the outer pipe 14 for maintaining the integrity of the borehole after extraction of the outer drill string rod is extracted from the borehole. The pipe may be also use as a casing to allow a prospecting probe to be lowered into the borehole to establish the composition of the formation in which the borehole has been drilled or for further drilling operation to extract, for example, core samples from the earth formation by lowering a core drill through the outer string 13 for generating a core sample. This is particular useful during diamond drilling.

The inner string rod 11 comprises (1) a plurality of inner tubes 12 sequentially attached as shown in FIGS. 12 a and 12 b and (2) a first inner tube 12 a adapted to receive a drill bit 92. Similarly, the outer string 13 is composed of (1) a plurality of outer tubes 14 sequentially attached as shown in FIGS. 12 a and 12 b and (2) a first outer tube 14 adapted to receive a drill bit 94.

Further, the inner string 11 is rotatably coupled to the outer string rod 13. This allows simultaneous rotation of the inner string rod 11 and the outer string rod 13 during drilling of the borehole. In an arrangement in accordance with the present embodiment of the invention, the rotational force is transferred from the swivel of the drilling rig to the outer string rod 13 and the outer string rod 13 transfers the rotational force to the inner string rod 11. The rotational force is transferred via a coupling.

In a particular arrangement, the coupling comprises a drive sub 96 and a driven gear 98. The drive sub 96 and the driven gear 98 are adapted to be attached, respectively, to the upper end of the first outer tube 14 a and the upper end of the first tube 12 a. Furthermore, the drive sub 96 and the driven gear 98 are adapted to be coupled together so as to transfer the rotational force from the outer string 13 to the inner string 11.

The drive sub 96 comprises a cylindrical body. The cylindrical body comprises an end having an inner threaded and an opposite end having an exterior thread. The end having the inner thread is adapted to be attached to the upper end of the first outer tube 14 a. The opposite end is adapted to be either (1) rotatably attached to the swivel for rotation of the drive sub 96 and the first outer tube or (2) attached to the additional outer tube 14 b (see FIG. 12 a). The opposite end is attached rotatably attached to the swivel during commencement of the drilling process. The opposite end is attached to the second additional outer tube 14 b after the borehole has been drilled to a depth of substantially the same than the length of the first outer tube 12 a incorporating the drive sub 96

FIG. 25 show a perspective view as seen from the box thread end of the drive sub 96. As shown in FIG. 25, the drive sub 96 comprises a plurality of indentations 100 arranged in a spaced apart relationship with respect to each other around the circumference of the inner surface of the cylindrical body of the drive sub 96. Each indentation 100 comprises a channel 102 and a locking area 104. The locking area 104 is an extended area having a width which is a greater than the width of the channel 102. Each extended area defines a pocket for securing a protrusion 106 of the driven gear 98 of the first inner tube 12 a.

The driven gear 98 comprises a cylindrical body adapted to be attached to the upper end of the first inner tube 12 a. The cylindrical body comprises an end having an inner threaded and an opposite end having an exterior thread. The end having the outer thread is adapted to be attached to the upper end of the first inner tube 12 a. The opposite end is adapted to be attached to the second additional outer tube 12 b (see FIG. 12 a).

The driven gear 98 comprises a plurality of protrusions 106 arranged in a spaced apart relationship around the outer circumference of the first inner tube 14. The protrusions 106 are adapted to be received by the locking area 104 of the drive sub 96 of the first outer tube 14 a.

As mentioned earlier, the drive sub 96 is adapted to be coupled to the driven gear 98 of the first inner tube 12 a to transfer the rotational force. The drive sub 96 is also adapted to enable uncoupling of the driven gear 98 to allow extraction of the inner string 11 from the outer string 13 after completion of the drilling process.

The coupling is accomplished when the first inner tube 12 a is inserted into the first outer tube 14 a. As the inner tube 12 a is inserted into the outer tube 14 a the protrusions 106 slide into the channels 102. To couple the inner tube 12 a and outer tube 14 a, the protrusions 106 are received by the locking area 104 of the drive sub 96. This is accomplished, by rotating the inner tube 12 a so that the protrusions 106 are driven into the locking area 104. To uncouple the inner tube 12 a from the outer tube 14 a, the inner tube 12 a is rotated—in the opposite direction than during the coupling process—so as to extract the protrusions 106 from the locking area 104 and the channels 102. In this manner, the inner tube 12 a may be selectively coupled and uncoupled from the outer tube 14 a.

Preferably, the drive sub 96 and the driven gear 98 are screwed, respectively, onto the upper end of the first outer tube 14 a and the upper end of the first inner tube 12 a. In this preferred arrangement the drive sub 96 and driven gear 98 are located at a location relatively distal to the drill bits 92 and 94. For example, the drive sub 96 and driven gear 98 are located at a distance of 4 meters from the drill bits 92 and 94. The fact that the drive sub 96 and driven gear 98 are located distal to the drill bits 92 and 94 avoids contamination of the drive sub 96 and driven gear 98 during the drilling process.

We refer now to FIGS. 1 to 5. FIGS. 1 to 5 show a drill rod 10 in accordance with an embodiment of the invention. As shown in FIG. 1, the outer tube 14 is adapted to receive the inner tube 12 defining the annulus 16 between the outer surface of the wall of the inner tube and the inner surface of the outer tube.

Referring now to FIG. 2, the inner tube 12 comprises a centre tube 18 and two end portions 20 and 22. Each end portion 20 and 22 is fastened to an end of the centre tube 18. As will be described with reference to the method of operation of the present rod assembly 10, the end portions 20 and 22 allows joining together inner tubes 12 to extend the overall length of the inner tube 12 as the drilling progresses and the depth of the borehole increases.

FIGS. 3 and 4 are perspective views of the end portions 20 and 22. The end portion 20 is the female end 20 (female junction) and the end portion 22 is the male end 22 (male junction). The female end 20 is adapted to receive a portion of the male end 20 to allow joining together two inner tubes 12 a and 12 b (see FIGS. 5 and 6). For this, the female comprises an open end 24 and the male end 22 comprises an open end 26. The open end 24 comprises an inner thread 28 which is adapted to receive the open end 26 of the male end 22. The open end 26 comprises an outer thread 30 and an extended portion 32. The extended portion 32 is adapted to be received within the open end 24 of the female end 20. The portion 32 extents into the open end 24 of the female end 20 until the outer thread 30 of the male end 22 joins the inner thread 28 of the female end 24. Rotating the male end 22 with respect to the female end 30 allows screwing the male end 22 to the female end 20. As will be described with reference to the method of operation of the present rod assembly 10 this allows joining together a plurality of inner tubes 12 (see FIGS. 5 and 6).

Referring back to FIGS. 3 and 4, the female and male ends 20 and 22 comprises opposite ends 32 and 34.

As shown in FIG. 3, the end 32 of the female end 20 and male end 22 comprises four sections 36 to 42. The first section 36 comprises an area indented with respect to the open end 24.

The second section 38 comprises an area having a plurality of protrusions 44. The protrusions 44 are arranged in a spaced apart arrangement around the circumference of the end portions 20 and 22. Each of the protrusions 44 extends radially outward from the circumference of the end portions 20 and 22. In the particular arrangement shown in the figures, the protrusions 44 extend beyond the circumference of the opened ends 24 and 26 such that the protrusions 44 are adapted to centre the inner 12 within the outer tube 14. In this manner, the arrangement of protrusions 44 defines a protruding structure to centre the inner 12 within the outer tube 14 defining the annulus 16 located between the inner tube 12 and the outer tube 14.

Further, the protrusions 44 are configured and arranged around the circumference of the opposite end 32 such that at least two clearances 46 are defined between the protrusions 44. In the particular arrangement shown in the figures, there are two clearances 46 a and 46 b located opposite to each other and there are defined two flat surfaces 48 between adjacent protrusions. The flat surfaces 48 are also opposite with respect to each other (see FIG. 4).

Referring back to FIG. 3, as mentioned before each protrusion 44 protrudes perpendicularly from the circumference of the end portions 20 and 22. In this manner, two surfaces 50 and 52 are defined which extend radially outward from the circumference of the end portions 20 and 22. The first surface 50 is a horizontal surface. In an arrangement, the first surface is a flat surface 50. The second surface 52 is an inclined surface.

As will be described with respect to the method of operation of the drill rod 10 in accordance with the present embodiment of the invention, the flat surface 50 facilitates holding and moving longitudinally the inner tube within the outer tube 12. This allows extraction of the inner tube 12 from the outer tube 14 as well as holding the inner tube 12 to avoid the inner tube 12 from falling into the outer tube 14 during, for example, joining of the inner tubes 12.

The flat surface 50 of the female end 20 faces opposite to the open end 24 of the female end 20. The flat surface 50 of the male end 22 faces opposite to the open end 26 of the male end 22. This particular arrangement of the flat surfaces 50 and 52 guarantees that both surfaces 50 and 52 faces towards the bottom of the hole. This is particularly advantageous in view that it allows, as mentioned earlier, holding and moving longitudinally the inner tube within the outer tube 12.

Holding and moving the inner tube 12 as well as joining inner tubes 12 together is accomplished via a snapper tool 60 (see FIG. 8). The snapper tool 60 is adapted to grab the inner tube 12. For this the snapper tool comprises jaws 62 for grabbing the inner tube 12. The jaws 62 are adapted to grab the inner tube 12 at, for example, at the indented first section 36 of any of the female end 20 or male end 22 (see FIGS. 9 to 11).

As mentioned above, the end portions 20 and 22 allows joining together inner tubes 12 to extend the overall length of the inner tube 12 as the drilling progresses and the depth of the borehole increases. FIGS. 5 and 6 shows the process for joining a pair of inner tubes 12.

In particular, FIG. 5 shows a first inner tube 12 a inside the outer tube 14. The inner tube 12 a is located within the outer tube 14 such that the open end 26 of the male end 22 extends out of the outer tube 14. The female end 20 of a second inner tube 12 b is presented to the male end 22 of the inner tube 12 a and moved longitudinally such that the open end 24 of the female end 20 receives the open end 26 of the male end 22. The female end 20 is moved longitudinally until the inner and outer screw 28 and 30 joins together. At this stage, the inner tube 12 b may be rotated so as to screw the inner tubes 12 a and 12 b together. As mentioned before, the inner tubes 12 a and 12 b may be grabbed via a snapper tool for rotating the inner tubes 12 a with respect to the 12 b (or vice versa) for joining the inner tubes 12 a and 12 b together. After joining the inner tubes 12 a and 12 b together, the inner tubes 12 a and 12 b may be moved longitudinally into the outer tube 14 to allow attachment of an additional inner tube 12 c (not shown). In this manner a plurality of inner tubes 12 may be joined together to extend the length of the inner tube 12 to account for the increasing depth of the borehole during drilling the drilling process.

As was explained before, in accordance with the present embodiment of the invention, the inner tubes 12 may be extracted from the outer tube 14. This is particularly advantageous in view that it allows the outer tube 14 to function as a casing for the borehole to allow prospecting probes to be lowered into the borehole. The process of extracting the inner tubes 12 is accomplished, for example, by grabbing the inner tubes 12 with the snapper tool and raising the inner tube 12 out of the outer tube 14. In a particular arrangement, the inner tubes 12 may be grabbed by the jaws 62 of the snapper tool 60 at the first section 26 adjacent the flat surface 50 of either the female end 20 or male end 22. In this manner, the flat surface 50 provides a support surface facilitating extraction of the inner tubes 12 when force is applied to the snapper tool 60 to move longitudinally the inner tube 12 out of the outer tube 14.

FIGS. 8 to 10 show the snapper tool 60 and the method for grabbing of the male junction 22. These figures show the method for grapping the male junction 22. However, the snapper tool 60 may grab the female junction 20 in a similar manner as shown in FIGS. 8 to 10.

In particular, FIG. 8 shows the snapper tool 60. The snapper tool 60 comprises a handle 64 and a head 66 attached to the handle 62. The head 64 comprises an indentation 66 which defines the jaws 62. The indentation 64 is located opposite the handle 64 of the snapper tool 60.

As shown in FIGS. 9 to 11, the indentation 66 is adapted to receive the flat vertical surface 48 defined by the protrusions 44. The fact that the indentation 66 receives the flat vertical surface 48 allows applying a rotational force to the inner tube during, for example, screwing the female and male junctions 20 and 22 during assembly of the extended inner tube 22.

Furthermore, the indentation 66 comprises a flange 68. In the particular arrangement shown in the FIGS. 9 to 11, the flange 68 extends all around the inner edge of the indentation. As shown in, for example, FIG. 9, the flange 68 is adapted to receive the flat surface 50 (defined by the protrusions 44). As was mentioned earlier with reference to method of operation of the drilling rod 10, the fact that the snapper tool 60 is adapted to receive the flat surface 50 allows holding the inner tube 12 to avoid that the inner tube 12 falls within the outer tube 14 during assembly of the extended inner tube 12. Also, the fact that the flat surface 50 is adapted to be received by the snapper tool 60 allows moving longitudinally the inner tube 12 with respect to the outer tube 14.

We refer now to FIGS. 12 a, 12 b and 15 to 26, As mentioned earlier, the inner string 11 is adapted to be releasably inserted in the outer string 13. This allows extraction of the inner string 12 after completion of the drilling process of the borehole without extracting the outer string 13 from the borehole.

FIG. 12 shows the drill rod 10. The drill rod 10 comprises a plurality of outer tubes 14 a to 14 c joined together and a plurality of inner tubes 12 a to 12 c inserted within the outer tubes 14. The inner tubes 12 b and 12 c are joined together via the female and male junctions 20 and 22. The inner tubes 12 a and 12 b are joined together via female and male junctions 70 and 72.

FIG. 12 a shows a schematic view of a lower section of the drilling rod in accordance with a first arrangement of the present embodiment of the invention showing the inner string 11 included in the outer string 13. In particular, FIG. 12 a shows the additional inner (12 b and 12 c) and additional outer tubes (14 b and 14 c) attached to the first inner and outer tubes 12 a and 14 a. The outer and inner string rod 11 and 13 is formed by joining together in an sequential manner the inner and outer rods 12 and 14 during the drilling process.

The drilling process starts by drilling the earth surface using the first and inner rod 12 a and 14 a. However, typically boreholes require to be of considerable more depth than the length of the inner and outer tube 12 a and 14 a. To drill boreholes of considerable more depth than the length of the inner and outer tube 12 a and 14 a it is necessary to join additional drilling rods 12 and 14 so as to extend the drilling string 11 and 13. The process of joining additional rods 12 and 14 is know as running the drill string into the well hole (also called borehole).

The running of the drill string into the well hole or the extracting of the drill string out of the well hole is performed using a tower-like structure (also called derrick). The derrick is located adjacent to the well hole during running of the drill string into the well hole

Typically, the derrick extends vertically from the well hole. The derrick comprises the drilling lines, pulleys and apparatus that allow running and extracting the drill string into and out of the well hole. The derrick also comprises the swivel for applying torque to the drill bits during drilling of the well hole.

Extending the length of the drill string is accomplished by detaching the upper end of the drill string from the swivel which provides the torque to the drill strings 11 and 13 formed by the inner and outer rods 12 and 14 that are within the borehole.

Prior detachment of the drill pipe from the swivel the drill string is fastened to the rotary table to impede that the drill string falls into the well hole. This is accomplished via a spanner 108 which extends perpendicularly from the derrick to the drilling string formed by the inner and outer rods 12 and 14. The spanner 105 is adapted to be displaced between a contracted condition and an extended condition. In the extended condition the spanner 105 secures the drill string to the rotary table 110.

After detachment of the drill string (defined by the inner and outer string 11 and 13) from the swivel, the swivel is lifted up along the derrick in order to add an additional inner and outer tubes 12 and 14 to the drill string. Lifting the swivel allows separating the swivel from the upper end of the drill string. This allows creating a clearance between the swivel and the upper end of the drill string to locate additional inner and outer tubes 12 and 14 to the upper end of the drill string. At this stage the additional outer rod 14—incorporating the additional inner rod 12—is located parallel to the derrick and lifted such that the additional inner and outer rods 12 and 14 are located above the tubes 12 and 14 to which the additional tubes 12 and 14 to be attached.

In order for the outer rod 14—incorporating the inner rod 12—be lifted without the inner rod 12 falling out of the outer rod it is necessary to temporary fasten the inner rod 12 to the outer rod 13. This accomplished via a threaded bracket 112—see FIG. 16. In the particular arrangement shown in the figures, the traversal cross section of the bracket 112 is configured as a horseshoe. This particular configuration of bracket 112 provides a gap extending parallel to the longitudinal axis of the bracket 112. The gap allows the bracket 112 to be extracted in a direction perpendicular to the longitudinal axis of the inner tubes 12.

FIG. 17 shows the inner tube 12 extending from the bracket 112 during lifting of the outer tube 14 prior attachment of the inner tube 12 to the drill string contained in the borehole.

Referring now back to FIGS. 15 a to 15 c, the outer tube 14 incorporating the inner tube 12 shown in FIG. 16 is located above the drill string located within the borehole for attachment to the drill string. The attachment process includes (1) attaching the additional inner tube 12 (the inner tube 12 to be added to the drill string for extension thereof) to the inner tube 12 of the drill string; (2) removing the bracket 11—see FIG. 15 b; (3) creating a clearance between the outer tubes 14 to enable the inner tube coupling to be tightened—see FIG. 15 c; and attaching the outer tube 12 to the drill string. At this stage, the spanner 108 is retracted to the contracted condition for the drilling process to continue. Attachment of additional inner and outer tubes 12 and 14 continues until the desired depth of the borehole is drilled.

Once the desired depth of the borehole has been reached the inner string 11 may be extracted from the outer string 13. This is accomplished by raising the inner string and separating the inner tubes 12 from each other—see FIGS. 20 to 23.

To separate the inner tubes 12 from each other, the inner string needs to be secured to the rotary table. This accomplished via the spanner 108 and an accessory spanner 113. The accessory spanner 113 is adapted to be mounted on the spanner 108—see FIG. 21. The function of the accessory spanner 112 is to secure the inner string 11 to impede the inner string 11 from rotating to stop inner from falling into the borehole. This allows releasing the inner tube 12 that is to be removed by applying torque to this particular inner tube 12 so as to unscrew the inner tube—see FIGS. 22 and 23. After unscrewing of the inner tube 12, the inner tube 12 can be removed. This process is repeated until the entire inner string 11 is removed from the interior of the outer string 13. To extract the first inner tube 12 a from the first outer tube 14 a the drives sub 96 and the drive means 96 are uncoupled from each other.

After removal of the inner string 11, the outer string 13 may be left inside the borehole. Alternatively, as was mentioned earlier, a pipe 90 may be introduced into the outer string and the outer string 13 may be extracted from the borehole in such a manner that the pipe 90 remains within the borehole. In an arrangement, the pipe 90 is kept as within the borehole acting as a casing to, for example, conduct analysis of the composition of the earth formation traversed by the borehole or for further drilling operation to extract, for example, core samples from the earth formation by lowering a core drill through the pipe 90 for generating a core sample. This is particular useful during diamond drilling.

In the previously described particular arrangement the inner string is releasably attached within the outer string.

In particular, the first inner tube 12 a of the inner string is releasably coupled to the drive sub 96 to allow transfer of rotational force from the outer string 13 to the inner string 11. Alternatively, the first inner tube 12 a may be fixed to the outer tube 14 a.

In the particular arrangement shown in FIG. 12 b, the inner tube 12 a is fixed within the outer tubes 14 a. Thus, the inner tube 12 a is not releasably secured within the outer tube 14 a as is the case with the inner tubes 12 b and 12 c which are adapted to be extracted from the outer tubes 12 after drilling of the borehole. The inner tube 12 a is attached to the inner tubes 12 b and 12 c via the female and male junctions 70 and 72.

The junctions 70 and 72 are adapted to be attached together in order to join the inner tube 12 a and the inner tube 12 together. The junctions 70 and 72 comprise internal seals which are adapted so that a relative large force is required to push the male junction 72 into the female junction 70. This arrangement impedes that the female and male junctions 70 and 72 be pulled apart easily. Also, the male junction 72 comprises lugs 74 and 76 defining a lug arrangement which stops the male junction 72 from turning when a rotational force is applied, for example, to the inner tubes 12 b and 12 c during assembly of the extended inner tube 12. This allows the junctions 20 and 22 to be tightened with a relative large force.

FIG. 13 shows the female junction 70 and the male junction 72. The female junction 70 comprises a first portion 76 and a second portion 78. The second portion 78 is of a reduced diameter with respect to the first section 76. The second portion comprises a plurality of lugs 74 arranged in a spaced apart relationship with respect to each other. In the particular arrangement, shown in FIG. 13, there are two pairs of lugs 74 a and 74 b located opposite to each other. In the arrangement shown in FIG. 13, there is shown only one pair of lugs 74 a and 74 b. The second pair of lugs (not shown) is located opposite to the lugs 74 a and 74 b. The lugs 74 are adapted to receive legs 80 a and 80 b of the male junction 72.

The male junction 72 comprises a first section 82 and a second section 84. The first section 82 is of reduced diameter with respect to the second section 84. The second section 84 is adapted to receive the second portion 78 of the female junction 70. And, as mentioned before, there are provided seals adapted so that relative large force is required to join together the female and male junctions 70 and 72 together.

Further, the male junction 72 comprises legs 80 a and 80 b which extend from the second section 84. The legs 80 are adapted to be received between the lugs 74 of the female junction 70. This can be seen in FIG. 14.

Referring back to FIG. 12, as mentioned before, the female and male junction 70 and 72 joins together the inner tubes 12 b and 12 c with the inner tube 12 a. After drilling has been completed, the inner tubes 12 b and 12 c (and any other additional inner tubes 12 which have been added to the inner tubes 12 b and 12 c to account for the increase of depth of the borehole during drilling thereof) are extracted from the plurality of outer tubes 14. The extraction is accomplished by separating the male junction 72 from the female junction 70 via pulling of the inner tubes 12 with the pull back of the drill rig. After separating the male and female junctions 70 and 72 the inner tubes 12 (except for the inner tube 12 a) can be treated as a rod string and using the spanner 60 ii is possible to unscrew and hold the inner tubes (that will be extracted from the outer tube) to stop them falling back down the borehole.

Modifications and variations as would be apparent to a skilled addressee are deemed to be within the scope of the present invention.

Further, it should be appreciated that the scope of the invention is not limited to the scope of the embodiments disclosed.

Throughout this specification, unless the context requires otherwise, the word “comprise” or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers. 

1. A drill rod for reverse circulation drilling, the drill rod comprising a first outer tube having an first end adapted to receive a rotational force to transfer the rotational force to the first drill bit and a second end adapted to receive a first drill bit, and a first inner tube adapted to be inserted in the outer tube to define an annulus to allow fluid flow from the first end of the outer tube to the second end of the outer tube, the inner tube having a first end and a second end, the second end being adapted to receive a second drill bit, wherein the inner tube is releasably inserted within the outer tube.
 2. A drill rod according to claim 1 further comprising a coupling for transferring the rotational force to the second drill bit, the coupling adapted to releasably couple the first inner tube to the first outer tube.
 3. A drill rod according to claim 2 wherein the coupling comprises a drive sub and a driven gear, the drive sub being releasably attached to the first outer tube and the driven gear being releasably attached to the first inner tube, the drive sub being adapted to releasably couple the inner tube to the outer tube
 4. A drill rod according to claim 3 wherein the drive sub is releasably attached to the first end of the first outer tube and the driven gear being releasably attached to the first end of the first inner tube.
 5. A drill rod according to claim 1 further comprising a seal between the second end of outer tube and the second end of the inner tube to impede fluid from exiting the annulus and the second end of the inner tube comprising at least one port to allow fluid to flow from the annulus into the inner tube to form a vacuum so as to transport soil samples into the inner tube to a location distal from the first and second drill bits.
 6. A drill rod according to claim 5 wherein the at least one port comprises an angled port to direct the fluid in a direction opposite to the first and second drill bits.
 7. A drill rod according to claim 1 wherein the first inner tube comprises a protruding structure to centre the inner tube within the outer tube.
 8. A drill rod according to claim 7 wherein the protruding structure comprises a plurality of protrusions extending radially outward from the circumference of the first and second ends, the protrusions being arranged in a spaced apart arrangement around the circumference of the first end second ends.
 9. A drill rod according to claim 8 further comprising a plurality of clearances between neighbouring protrusions and a plurality of surfaces between neighbouring protrusions, the clearances being located opposite to each other and the surfaces being located opposite to each other.
 10. A drill rod according to claim 3 further comprising a plurality of second inner tubes adapted to be sequentially attached to each other and to the driven gears, and a plurality of second outer tubes adapted to be sequentially attached to each other and to the drive sub.
 11. A drill rod according to claim 10 wherein each of the second inner tubes comprises the protruding structure for centring the inner tubes within the outer tubes.
 12. An inner string of a drill rod for reverse circulation drilling, the inner string comprising an inner tube, the inner tube being adapted to be releasably inserted in an outer tube, the inner tube and the outer tube defining an annulus between the inner and the outer tube.
 13. An inner string according to claim 12 wherein the inner tube comprises first and second ends, the first and second ends comprising a protruding structure for centring the inner tube within the outer tube,
 14. An inner string according to claim 12 further comprising a driven gear having an end attached to the first end of the inner tube, the driven gear being adapted to receive a rotational force from the outer tube for rotation of a drill bit attached to the second end of the drill bit.
 15. An inner string according to claim 14 wherein the driven gear is adapted to releasably couple the inner tube to the outer tube.
 16. An inner string according to claim 14 further comprising at least one additional inner tube comprising a protruding structure for centring the additional inner tube within an additional outer tube, the driven gear having an opposite end attached to the additional inner tube.
 17. An inner string according to claim 12 wherein the second end of the inner tube comprises at least one port to allow fluid to flow from the annulus into the inner tube to define a vacuum at a location adjacent the second end of the inner tube.
 18. An inner string according claim 17 wherein the at least one port comprises an angled port.
 19. A method for casing a borehole after drilling thereof, the method comprising the steps of: inserting at least one first inner tube in an outer tube having a lower end adapted to receive a first drill bit, the inner tube having a lower end adapted to receive a second drill bit; releasably coupling the inner tube to the outer tube to transfer rotational force from the outer tube to the second drill bit; drilling the borehole using the outer tube incorporating the inner tube; and extracting the inner tube from the outer tube.
 20. The method according to claim 19 further comprising the steps of inserting a pipe within the outer tube and extracting the outer tube. 